This invention relates generally to the depositing of loose materials into a storage hopper, and more particularly to a variable height charging system for depositing fragile pellets made of fly ash.
Material storage devices such as silos have long been used to store particulate and loose materials such as grains, and other similar objects. Typically the material to be stored in the silo is loaded into the silo through an opening in the top and is discharged from the silo through a chute in the bottom of the silo. The material as it enters from the top generally falls freely down to the level of previously deposited material. This free fall can be acceptable for certain materials, such as grains which are not particularly fragile or where the fragmentation of the material being stored does not present a problem. There are, however, associated problems with the creation of dust and the nonuniform depositing of the material throughout the silo.
There are several devices, known well in the art, for limiting the speed of the fall of the material being stored which helped to control dust and degradation of the material. For example, U.S. Pat. No. 1,720,822 discloses a telescoping tube extending down the center of the storage bin which can be used through which the material is allowed to free fall to the bottom until the telescoping tube is filled to a level near the top of the tube. Once the level has reached a sufficient height, the material added to the telescoping tube free falls only a short distance to the top of the material in the tube. As more material is added through the tube, the lower sections of the tube are raised, allowing the material at the bottom of the tube to flow from the tube into the storage bin. Thus, the operator can control the height of the material within the tube, and consequently the free fall distance, by the fill rate and the rate that the telescoping tube is raised. As long as a sufficient flow of material is supplied to the tube, newly deposited material can have a relatively short free fall distance. This results in less dust and breakage of the material at the top of the tube. However, as the bottom of the tube is raised, the material flows in a somewhat uncontrollable manner as the exit plane of the telescoping tube is raised above the level of the material in the silo. This results in the creation of dust and breakage of the material at the bottom level. Another problem with this type of device is that the telescoping tube must be filled to a certain height before the free fall of the material can be limited to a short distance. This initial fill of the tube allows the material to free fall the entire length of the silo, resulting in dust and breakage. Furthermore, a telescoping tube of this nature permits the material to remain within the tube between periods of silo changing. Hence, such a system is unsuitable for handling materials that might agglomerate in the tube.
An additional problem with the above described device is the inability to fill the silo all the way to the top. As the telescoping tube retracts, part of it can remain within the silo, even while in its fully retracted position. To resolve this problem a helical chute was added in U.S. Pat. No. 1,968,071 to allow the last portion of the silo to be charged by flowing the material down the chute once the tube had fully retracted. This system has all the disadvantages described above as well as problems with the chute, as described below.
The use of helical chutes which extend all the way to the bottom of the silo is also well known in the art. The angle of the chute must be sufficiently steep so as to allow the material to exit the chute when it reaches the level of material already deposited in the silo. If this angle is too shallow, the material will back up on the chute itself and not discharge at the lower end onto the other material. Once the material has backed up the chute to the fill point of the silo, any additional material is either blocked from entering the silo or simply bypasses the chute, free falling the length of the silo down to the level of material previously deposited.
If the slope of the chute is too great, material flowing down the chute will create dust and also be subjected to degradation. In some cases, depending on the nature of the material to be deposited in the silo, it is impossible to select an angle for the chute which allows the material to flow from the chute at the bottom while not flowing so fast that it creates dust and damages the material. With such material it is necessary to use an alternate method for filling the silo.
There are also devices well known in the art for uniformly distributing material in a silo, some of which are shown in U.S. Pat. Nos. 3,182,859; 3,473,677; and 3,524,557. These devices may take several forms. The charging system may be located Permanently at the top of the silo or storage bin and deposit the material into partitioned compartments of the silo to control the fill of each individual section. Such a system may have a conveyor belt located on tracks at the top of the silo where the ends of the conveyor belt may be shuttled from side to side and the direction of rotation of the conveyor belt may be changed to fill particular compartments. Other systems may be located within the silo itself and used to distribute material from the center of the silo to the outer edges, by use of a conveyor system such as an auger. In the prior art, these systems are used by allowing the material to free fall down to a hopper located at the level of the previously filled material and are thereafter distributed to the edges of the silo by the auger. Both of these systems do not solve the problem of the free fall of the material described above. Dust is created and degradation of the material results from the free fall.
Various types of material may be stored in silos or storage bins. In particular, pellets which are made from fly ash generated by a coal furnace may be so stored for curing. Immediately after formation, these pellets are soft and fragile and need to cure before they can be handled. It is preferred to store these green pellets in a silo at the site of the furnace, where they are cured sufficiently for transportation to another site.
After the pellets have initially been formed, they are very fragile and moist. If they are subjected to a free fall, such as described in the prior art above, they will break into even smaller Particles and tend to agglomerate together. If pellets are loaded into a silo for curing using a system which allows them to break up and agglomerate, the pellets become very difficult, if not impossible to remove them, through the discharge chute at the bottom of the silo. Furthermore, the free fall and degradation of the pellets results in the creation of fly ash dust which must be contained due to air pollution control standards. Thus, a system is needed to deposit fly ash pellets and the like into a storage silo or bin which eliminates these problems.